Quantification of a specific macromolecule (the “target”), particularly in the presence of other components, such as, a specific protein on the cell surface, in a protein mixture, in a cell homogenate, is commonly performed with use of an antibody that specifically recognizes the target. In general, the protein mixture is first immobilized on a support, for example, by adsorption or covalent linkage to a membrane or a plastic surface, or to a support surface to which an antibody specific for the target (“immobilizing antibody”) has been attached, and exposed to a target-specific antibody (“primary antibody”, different from the immobilizing antibody, if one was used). After an appropriate reaction time, excess primary antibody is removed by repeated washes, and the amount of bound antibody is determined by one of several methods. For example, the primary antibody may have been covalently linked to a fluorescent tag, and may be detected by measuring the intensity of fluorescence; alternatively, a “secondary” antibody (tagged with a marker, such as a fluorescent dye or an enzyme) directed against the primary antibody, may be used for quantification. Many different approaches for the quantification of the primary antibody are available, but common to all is the requirement that any primary or secondary antibody that is not bound to the target be completely removed, because it would give rise to a signal indistinguishable from that of specifically bound antibody. Because high-throughput screening does not allow for washing steps, the above-mentioned approaches are not applicable.